Antileukemic therapy is designed to obtain maximum cell kill. Frequently, a reduced number of functional platelets and leukocytes are present at the start of therapy only to be destroyed as one administers cytotoxic agents. This project is designed to determine if the cytotoxic effect of chemotherapy against platelet precursors can be selectively attenuated by platelet hypertransfusion. The dog which behaves similar to man in its response to platelet transfusion will be used as a working model.